Author Topic: Mars Crew Landers - Two Stage or Single Stage?  (Read 20888 times)

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 28186
  • Minnesota
  • Liked: 7982
  • Likes Given: 5331
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #20 on: 10/23/2016 12:03 AM »
Sure, we all understand that. When people say SSTO they should say it accomplishes its mission without staging.

And the advantage for a lunar lander or any vehicle is that fewer stages mean fewer interfaces and fewer vehicle configurations to analyze and develop. It might even mean a safety improvement since there are fewer components (and also because failures often happen at staging events).

But anyway, since we aren't stuck with making things expendable, we can also say that single stage makes reuse WAY easier until your delta-v is around twice your exhaust velocity.

For the Moon that means you can refuel the reusable lander in orbit.

Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Pipcard

  • Full Member
  • ****
  • Posts: 476
  • Liked: 120
  • Likes Given: 98
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #21 on: 10/23/2016 12:11 AM »
Sure, we all understand that. When people say SSTO they should say it accomplishes its mission without staging.

And the advantage for a lunar lander or any vehicle is that fewer stages mean fewer interfaces and fewer vehicle configurations to analyze and develop. It might even mean a safety improvement since there are fewer components (and also because failures often happen at staging events).

But anyway, since we aren't stuck with making things expendable, we can also say that single stage makes reuse WAY easier until your delta-v is around twice your exhaust velocity.

For the Moon that means you can refuel the reusable lander in orbit.
I agree with your logic, and anything reusable should have as few stages as reasonably possible (e.g. one stage for a reusable lunar lander, and the two-stage ITS - upper stage getting fueled in LEO, taking that all the way to the Martian surface, where it gets refueled again for the return trip).

But how do you explain this Spaceworks study in which they concluded that the development costs for a two-stage and single stage lunar lander were almost the same? And yes, reliability was higher, but only slightly; separation only contributed a very small part to risk.
« Last Edit: 10/23/2016 12:17 AM by Pipcard »

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 28186
  • Minnesota
  • Liked: 7982
  • Likes Given: 5331
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #22 on: 10/23/2016 12:54 AM »
Sure, we all understand that. When people say SSTO they should say it accomplishes its mission without staging.

And the advantage for a lunar lander or any vehicle is that fewer stages mean fewer interfaces and fewer vehicle configurations to analyze and develop. It might even mean a safety improvement since there are fewer components (and also because failures often happen at staging events).

But anyway, since we aren't stuck with making things expendable, we can also say that single stage makes reuse WAY easier until your delta-v is around twice your exhaust velocity.

For the Moon that means you can refuel the reusable lander in orbit.
I agree with your logic, and anything reusable should have as few stages as reasonably possible (e.g. one stage for a reusable lunar lander, and the two-stage ITS - upper stage getting fueled in LEO, taking that all the way to the Martian surface, where it gets refueled again for the return trip).

But how do you explain this Spaceworks study in which they concluded that the development costs for a two-stage and single stage lunar lander were almost the same? And yes, reliability was higher, but only slightly; separation only contributed a very small part to risk.
Yeah, if you're operating expendably, there's not a huge difference. But also, I don't always trust analyses. I think the multiple configurations thing makes a bigger difference to cost than people realize, especially if we're talking about like half a dozen vehicle configurations, like MSL and skycrane (from cruise phase down to the surface, there's like 6 or 7 different vehicle configurations in flight!).

I also tend to think that good landers should be built a bit like launch vehicle stages with legs, i.e. very efficient shapes (common bulkhead, with the propellant tanks themselves carrying the loads, perhaps even partially pressure-stabilized) with a bare minimum in parasitic mass. That makes single-stage a lot easier performance-wise, and dramatically reduces the benefit of splitting a vehicle into two stages. The Spaceworks study doesn't use that kind of mass-efficient sort of lander in their parametric analysis, so it makes single-stage look not as attractive as it should be.

I generally find the mass ratio assumptions to be worse in these kinds of parametric studies than is realistically achievable. (And they do this for the sake of conservatism and excuse it by saying they're doing so consistently.) That inevitably pushes things toward a lot more staging events, vehicle configurations, and expendability. And with so many interfaces to deal with, mass growth is inevitable, kind of becoming a self-fulfilling prophecy.

In general, I prefer vehicles to not shed parts as they go through the mission. Fewer interfaces and fewer things to go wrong, and gives you the opportunity to focus on improving the mass ratio through efficient structural design.
« Last Edit: 10/23/2016 12:57 AM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 981
  • Likes Given: 343
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #23 on: 10/23/2016 01:18 AM »
First things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?
When your maximum feasibly achievable ISP is ~325, it's not like you have much of a choice
Orion - the first and only manned not-too-deep-space craft

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 28186
  • Minnesota
  • Liked: 7982
  • Likes Given: 5331
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #24 on: 10/23/2016 02:13 AM »
First things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?
When your maximum feasibly achievable ISP is ~325, it's not like you have much of a choice
That's not at all true. A reusable single stage lander/ascender is perfectly feasible with bipropellant hypergols, which are basically indefinitely storable and have very good density. 5km/s is more than enough delta-v and that is perfectly feasible with a high performance lander. Especially since you only need legs, not a heatshield.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Warren Platts

Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #25 on: 10/29/2016 01:54 AM »
That's the thing: if you have a relatively-easily-produced, abundant source of ISRU propellant at both ends (Mars surface to LMO), the SSTO lander could be fully propulsive, simplifying design. Heck, a beefed-up, ACES-style lunar lander could do it. Might want to substitute a titanium skin for the aluminum.

What's less clear is why one would want to mine water only to covert it to methane for the SSTO lander? We know very well how to handle liquid hydrogen--that's no showstopper--and once you have LH2, you get your oxygen cooling for free.

If it's high thrust you want, one could possibly make an Al, O2, tripropellant that would have the Isp of LH2/LO2 with the thrust of ALLOX monopropellant rockets. Probably in practice it would be a sort of ALLOX/LH2 bipropellant (with powdered aluminum mixed into a LO2 gel to form the ALLOX).
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Hanelyp

  • Full Member
  • ***
  • Posts: 369
  • Liked: 65
  • Likes Given: 252
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #26 on: 10/30/2016 03:06 AM »
If water is a harder to come by resource, combining it with CO2 to produce methane and O2 lets you get more propulsion from your water.  As for aluminum based propellants, power fuels are hard to handle, and more than a tiny amount of Al2O3 in the exhaust presents problems, especially if you want a reusable engine.  An aluminum/LOX gel strikes me a a potential very big boom if it encounters a sufficient ignition source.  Aluminum gelled in the fuel component should be much safer.

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 4312
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 1096
  • Likes Given: 2094
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #27 on: 10/30/2016 03:19 AM »
I've often wondered if a Hydrazine/LOX mix would be okay - the Lander descends with an excess of hydrazine leftover after landing. Then; LOX is made by splitting CO2 and liquifyng it. This makes up the ascent propellant then - whoosh - off they go! :)
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline Impaler

  • Full Member
  • ****
  • Posts: 1283
  • South Hill, Virgina
  • Liked: 363
  • Likes Given: 0
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #28 on: 10/30/2016 06:04 AM »
I've often wondered if a Hydrazine/LOX mix would be okay - the Lander descends with an excess of hydrazine leftover after landing. Then; LOX is made by splitting CO2 and liquifyng it. This makes up the ascent propellant then - whoosh - off they go! :)

A very original idea, whether or not Hydrazine and LOX are hypergolic together is key if they aren't then the same engine cant be used for the descent and assent.

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 4312
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 1096
  • Likes Given: 2094
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #29 on: 10/30/2016 08:45 AM »
No; they would not be hypergolic. But hydrazine mixed with LOX would still be decently powerful stuff - vacuum specific impulse better than 330 seconds if pressure fed, rising to more than 350 seconds if pump fed. A multi-redundant sparkplug system could be used for ignition with perhaps 'cartridge' starters for 'failsafe' on ascent duites. And the type of hydrazine used would more likely be MMH.
« Last Edit: 03/06/2018 11:22 PM by MATTBLAK »
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 4312
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 1096
  • Likes Given: 2094
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #30 on: 10/30/2016 09:12 AM »
I've been thinking about a relatively simple single stage dual-purpose vehicle: a Mars Descent/Ascent Vehicle (pronounced 'EmDav') - well, as simple as a manned Mars lander is ever gonna get anyway! If the surface Habitat is a pre-landed, seperate vehicle, then the MDAV can be just large enough to land a small crew of three or four Astronauts in a small cabin, surrounded by propellant tanks, legs and the engines. Prior to landing, it would have an ejectable aeroshell, a stabilizing parachute(s) and to keep the mass low for ascent later - maybe even propellant drop tanks or a 'crasher' stage. As well as a separately landed Habitat there would have to be a landed Power/ISRU Module (PIM). I'm envisaging a Solar/RTG/Stirling system that will split CO2 from the Martian air and pump it into the MDAV LOX tanks. Either the MDAV would have to be landed close to the PIM, or the PIM could actually be a Rover - capable of driving itself or being driven over to the MDAV by the crew.

Power cables could be run over to the Habitat, or the PIM rolls to the Hab when it's filled the MDAV's LOX tanks. In any case, the Habitat should be fitted with it's own solar arrays, augmented by a couple RTGs and batteries for night time duties.
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline Oli

  • Senior Member
  • *****
  • Posts: 2193
  • Liked: 407
  • Likes Given: 57
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #31 on: 10/30/2016 10:30 AM »
No; they would not be hypergolic. But hydrazine mixed with LOX would still be pretty flammable stuff - vacuum specific impulse better than 330 seconds if pressure fed, rising to more than 350 seconds if pump fed. A multi-redundant sparkplug system could be used for ignition with perhaps 'cartridge' starters for 'failsafe' on ascent duites. And the type of hydrazine used would more likely be UDMH.

What Impaler wants to say is that developing multiple in-space engines for the lander alone is a no-go. Ideally you want the same chemical in-space engine for your entire Mars architecture.

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 4312
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 1096
  • Likes Given: 2094
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #32 on: 10/30/2016 07:44 PM »
Some families of engines have run multiple propellant types in tests. In a lot of Mars architecture studies, the RL-10 family has shown versatility, using either LOX/LH2 or LOX/CH4. Having just one family of engines for the whole In-space operations may not be practical - some can be fixed thrust but for Mars EDL, the engines would basically have to be throttling. There can be big differences between fixed and throttling versions of engines. There are four main propellant families that we know can work: hypergolics, LOX/RP1, LOX/LH2 and LOX/CH4. We need a lot more experience with methane, but I have a feeling that's coming soon!

It will probably be LOX/LH2 for Earth departure - because a lot of mass in a deep gravity well needs to be moved out as efficiently as possible - which is why Solar Electric Propulsion has also reared it's head in Mars Architecture studies of late. For in space propulsion over long periods, we know that hypergolics have been King. A variation in the engine design for in space and the Mars Descent & Ascent Vehicles could be done - LOX ISRU on Mars is a heck of a lot easier than producing Nitrogen Tetroxide there, I'm picking. ;)
« Last Edit: 10/31/2016 12:32 AM by MATTBLAK »
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline Paul451

  • Full Member
  • ****
  • Posts: 1407
  • Australia
  • Liked: 685
  • Likes Given: 584
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #33 on: 12/07/2016 02:53 AM »
Is there an existing nomenclature that differentiates between an SSTO ascent vehicle that is landed on a descent stage, vs an SSTO that is self-landing, vs a genuine TSTO ascent vehicle?
« Last Edit: 12/08/2016 06:53 AM by Paul451 »

Offline Russel

  • Full Member
  • ****
  • Posts: 983
  • Liked: 91
  • Likes Given: 1
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #34 on: 12/08/2016 02:08 AM »
Having skimmed this thread I must say that I'd still prefer a fully propulsive lander specialised for crew landing.

Main reason being simplicity, reliability (risk) and low g forces. With modern materials such a lander can be robust yet relatively light.

The same vehicle could be used as an ascent vehicle. Whether that means actual reuse or commonality in design is another question.

I don't like designs that are inherently high g force or involve multiple configurations and parachutes.

What I would warm to is a design rather like Musk's "land on tail glider". But with higher surface to mass ratio and scaled down as a crew only lander. Again I don't like his proposed 4-6 gs but that could be lowered to under 3g with a larger surface to mass.

Offline colbourne

  • Full Member
  • ***
  • Posts: 339
  • Liked: 41
  • Likes Given: 17
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #35 on: 12/09/2016 11:17 AM »
I would have thought it best to design the lander/ascent craft  to use cheap expendable solid fuel boosters. These give the best of both SSTO and multi stage designs.

Offline R7

  • Propulsophile
  • Senior Member
  • *****
  • Posts: 2738
    • Don't worry.. we can still be fans of OSC and SNC
  • Liked: 949
  • Likes Given: 662
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #36 on: 12/09/2016 11:50 AM »
Is there an existing nomenclature that differentiates between an SSTO ascent vehicle that is landed on a descent stage, vs an SSTO that is self-landing, vs a genuine TSTO ascent vehicle?

The last one differentiates itself from the other two by definition, 2 stages != 1 stage.
The middle case seems to lack catchy acronym. SSTAFO? (single stage to and from orbit)
AD·ASTRA·ASTRORVM·GRATIA

Offline rocx

  • Full Member
  • ***
  • Posts: 385
  • NL
  • Liked: 265
  • Likes Given: 145
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #37 on: 12/09/2016 12:03 PM »
I would have thought it best to design the lander/ascent craft  to use cheap expendable solid fuel boosters. These give the best of both SSTO and multi stage designs.

Solid boosters have the worst Isp, which really hurts in a stage that you have to take with you all the way through launch, escape burn, capture and landing. Better is to have a mass efficient stage. Even better is to produce the fuel locally.
Any day with a rocket landing is a fantastic day.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32333
  • Cape Canaveral Spaceport
  • Liked: 10991
  • Likes Given: 327
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #38 on: 12/09/2016 01:25 PM »
I would have thought it best to design the lander/ascent craft  to use cheap expendable solid fuel boosters. These give the best of both SSTO and multi stage designs.


They provide the worse for both designs.
« Last Edit: 12/09/2016 01:25 PM by Jim »

Offline clongton

  • Expert
  • Senior Member
  • *****
  • Posts: 10516
  • Connecticut
    • Direct Launcher
  • Liked: 2530
  • Likes Given: 910
Re: Mars Crew Landers - Two Stage or Single Stage?
« Reply #39 on: 12/09/2016 06:29 PM »
What's less clear is why one would want to mine water only to covert it to methane for the SSTO lander? We know very well how to handle liquid hydrogen--that's no showstopper--and once you have LH2, you get your oxygen cooling for free.

Because water and CO2 are readily available and LOX/CH4 engines are far less complex than LOX/H2 engines. Not to mention that LOX/CH4 IC engines may well become the ground transportation mode of choice (speculation of course). That would provide the advantage of a single-fuel economy.
« Last Edit: 12/09/2016 06:36 PM by clongton »
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine